What is Strongyloidiasis and Why Should You Care?

Parasitic infections are amongst those groups of infections that are most often neglected in public health discussions, especially in more developed countries. However, there are certain infections that remain dangerously overlooked, even though they can lead to severe or fatal outcomes if left untreated. One such disease is strongyloidiasis, which is a condition that is caused by a nematode (roundworm) known as Strongyloides stercoralis. Although it may seem quite obscure, this infection is both common and also potentially life-threatening, particularly in several immunocompromised individuals.

In this blog, we will explore the key aspects of strongyloidiasis, from what it is, and how it spreads, its symptoms, diagnosis, and also treatment options, hence culminating in why this disease should be on your radar, whether you are a health professional, traveler, or just simply someone concerned with global health.

What is Strongyloidiasis?

Strongyloidiasis is a parasitic infection that is caused by the nematode Strongyloides stercoralis, and in some cases, Strongyloides fuelleborni. It is a soil-transmitted helminth, which means that the infection typically begins when the larvae present in contaminated soil penetrate the human skin. Unlike many other parasitic infections, Strongyloides has a very unique life cycle that includes the ability to reproduce within the human host, a phenomenon that is called autoinfection. This further allows the infection to persist for decades, even without any re-exposure.

The autoinfection cycle is what makes Strongyloides especially dangerous because it can cause hyperinfection or even disseminated disease in certain individuals. In case of hyperinfection, the parasite burden increases dramatically and it also invades other organs that are outside of its usual habitat in the gastrointestinal tract. Disseminated disease can also virtually affect any organ and is hence often fatal.

While strongyloidiasis is typically endemic in tropical and subtropical regions—including parts of Africa, Southeast Asia, Latin America, and the southeastern United States—global travel and migration patterns have contributed to cases emerging worldwide.

How is Strongyloidiasis Transmitted?

The primary mode of transmission for Strongyloides stercoralis is skin contact with contaminated soil. The infectious larvae (filariform larvae) present in soil penetrate human skin—often through the feet when walking barefoot. This is the start of a complex life cycle that sets Strongyloides apart from many other parasitic worms.

The Lifecycle:

1. Skin Penetration: Infective larvae penetrate the skin.

2. Migration: Larvae travel through the bloodstream to the lungs, then ascend the respiratory tract to the throat, where they are swallowed.

3. Intestinal Colonization: Once swallowed, the larvae reach the small intestine, mature into adult females, and embed in the mucosa to produce eggs by parthenogenesis (without mating).

4. Larval Development: Eggs hatch into rhabditiform larvae that are excreted in feces or transform into infectious filariform larvae inside the host, causing autoinfection.

Autoinfection allows the parasite to maintain a long-term presence in the host without needing to return to the external environment. This is especially concerning because reinfection can occur internally, potentially leading to chronic and asymptomatic infections that go unnoticed for years.

Other Transmission Routes:

• Organ transplantation: In rare cases, strongyloidiasis has been transmitted through organ transplants.

• Mother-to-child transmission: Although uncommon, there are instances where vertical transmission may occur.

Risk factors for infection include:

• Walking barefoot in endemic areas

• Poor sanitation and hygiene

• Immunosuppressive therapy (e.g., corticosteroids, chemotherapy)

• HIV/AIDS or other immunocompromised states

Symptoms of Strongyloidiasis

Strongyloidiasis is often dubbed a “silent” infection because many people show no symptoms or experience mild, nonspecific complaints. However, when symptoms do appear, they can range from mild gastrointestinal distress to life-threatening systemic complications.

Acute Infection:

• Skin: Localized rash or urticaria (often on the feet or entry point)

• Pulmonary: Dry cough, wheezing, or shortness of breath due to larval migration through the lungs (similar to Loeffler’s syndrome)

• Gastrointestinal: Nausea, diarrhea, abdominal pain, bloating

Chronic Infection:

In immunocompetent individuals, the infection may remain in a chronic, smoldering state for years. Symptoms may include:

• Intermittent diarrhea and constipation

• Abdominal pain or discomfort

• Weight loss

• Eosinophilia (elevated eosinophil count in blood tests)

Hyperinfection Syndrome:

This occurs when the parasite proliferates extensively due to weakened immunity—especially after immunosuppressive therapy.

• Severe diarrhea and malabsorption

• Worsening respiratory symptoms (due to larval migration to the lungs)

• Sepsis: Bacterial infections can accompany hyperinfection as larvae carry intestinal bacteria into the bloodstream.

Disseminated Strongyloidiasis:

In this advanced and often fatal form, larvae travel beyond the GI and respiratory systems to organs like the brain, liver, and kidneys.

• Neurological symptoms (confusion, seizures)

• Multi-organ failure

• Shock

Mortality in disseminated cases can exceed 85% if not treated promptly.

Diagnosis of Strongyloidiasis

Diagnosing strongyloidiasis can be challenging due to its often asymptomatic nature and intermittent larval shedding. Conventional stool tests can miss the diagnosis if only one sample is tested.

Common Diagnostic Methods:

1. Stool Microscopy:
   • Detection of rhabditiform larvae in fresh stool samples.

   • Requires multiple samples over several days to increase sensitivity.

2. Serological Testing:
   • Enzyme-linked immunosorbent assay (ELISA) detects antibodies against Strongyloides.

   • High sensitivity and specificity, especially useful in non-endemic areas.

3. Larval Culture Techniques:
   • Agar plate culture to detect motile larvae.

   • More sensitive than direct microscopy.

4. Molecular Testing (PCR):
   • Polymerase Chain Reaction (PCR) assays can detect Strongyloides DNA.

   • Not widely available but increasingly used in research and advanced labs.

5. Biopsy:
   • In rare cases, larvae may be seen in tissue biopsies during endoscopy.

6. Eosinophilia:
   • Persistent eosinophilia in the blood may be a clue, though it is not specific.

Diagnosis becomes particularly urgent before initiating immunosuppressive treatments, especially in individuals from endemic regions.

Treatment Options

The treatment of strongyloidiasis is generally straightforward in uncomplicated cases but becomes more complex in disseminated or hyperinfection syndromes.

First-Line Therapy:

Ivermectin:

• Dosage: 200 μg/kg orally, once daily for 1–2 days for uncomplicated infection.

• Effectiveness: High cure rates in most patients.

• Mechanism: Paralyzes the parasite by interfering with its nervous system.

Alternative Medications:

• Albendazole:
  • Less effective than ivermectin.

  • 400 mg twice daily for 7 days is typically recommended.

  • Used when ivermectin is not available or contraindicated.

Treatment for Hyperinfection/Disseminated Disease:

• Extended Ivermectin therapy: Given daily until stool and/or sputum exams are negative for 2 weeks.

• Parenteral Ivermectin (investigational): Considered in patients unable to take oral medications.

• Supportive therapy: Includes managing sepsis, respiratory failure, and electrolyte imbalance.

• Antibiotics: Often required due to secondary bacterial infections.

Screening before immunosuppression:
Prophylactic ivermectin is often administered in high-risk patients before starting corticosteroids or chemotherapy, especially if they are from endemic regions or have eosinophilia.

Conclusion

Strongyloidiasis is a neglected yet impactful parasitic disease that warrants more attention, especially given its ability to cause lifelong infection and deadly complications. Its unique lifecycle, especially the capacity for autoinfection, distinguishes it from many other parasitic infections and contributes to its potential severity in immunocompromised individuals.

The disease often flies under the radar, particularly in non-endemic areas, but globalization and migration trends mean clinicians and public health professionals everywhere must remain vigilant. Travelers, healthcare providers, and even immunosuppressed patients themselves should be aware of the risks and symptoms associated with this infection.

FAQs 

1. Can strongyloidiasis go away on its own without treatment?

No, strongyloidiasis typically does not resolve on its own due to the parasite’s unique ability to reproduce inside the human host (autoinfection). This allows the infection to persist for decades, and in some cases, it may worsen and become life-threatening, especially in immunocompromised individuals.

2. Who is most at risk of developing severe strongyloidiasis?

Individuals with weakened immune systems—such as those taking corticosteroids, undergoing chemotherapy, or infected with HIV/AIDS—are at the highest risk. In these patients, the infection can develop into hyperinfection syndrome or disseminated strongyloidiasis, both of which carry high mortality rates.

3. How can I prevent getting infected with Strongyloides stercoralis?

Prevention measures include:

• Wearing footwear in areas with contaminated soil (especially in tropical and subtropical regions)

• Avoiding contact with untreated sewage or fecally-contaminated soil

• Practicing good hygiene and sanitation

• Screening and prophylactic treatment before immunosuppressive therapies in high-risk populations

4. Is there a test to confirm strongyloidiasis even if I don’t have symptoms?

Yes. Serological tests (like ELISA) are highly effective in detecting Strongyloides antibodies, especially in people without active symptoms. If you’ve lived in or traveled to an endemic area and have persistent eosinophilia, it’s wise to request a screening test.

5. What is the best treatment for strongyloidiasis?

The first-line treatment is Ivermectin, usually given as 200 μg/kg orally for 1–2 days in uncomplicated cases. For severe infections, daily treatment continues until the infection clears, as confirmed by stool or sputum tests. In some situations, Albendazole may be used as an alternative, though it’s less effective.